Numerous applications exist for turbomachinery, such as turbochargers used in automotive applications and gas turbine engines utilized in various military and aerospace vehicles. An example is the turbofan engine, which is used to propel aircraft at subsonic and supersonic speeds. For subsonic speeds, high bypass turbofan engines are often employed. These engines include a large fan which is typically placed at the front of the engine. The fan serves to produce greater thrust and reduce specific fuel consumption. As with most turbomachinery, such fans are circumferentially enclosed by a containment casing which is specifically designed to be capable of containing a fan blade in the event that the fan blade is released from its hub during operation. As a result, the containment casing is able to minimize the structural damage to the engine and aircraft if one or more fan blades are released from the hub due to a catastrophic failure of one or more blades.
A unique problem arises when a fan blade is released during the operation of the engine in a manner that causes the fan blade to strike the containment casing in a region forward of the fan, as illustrated in FIG. 1. Such an event is likely to occur when a first blade fails and strikes a second trailing blade such that the second blade is propelled forward from the fan. Fan blades released in this manner are more difficult to contain than when a released blade remains within the plane of the fan because, as shown in FIG. 1, the resulting impact is relatively localized. Typically, under such circumstances essentially all of the kinetic energy of the fan blade is dissipated at the aft corner of the blade. As a result, the blade is more apt to inflict severe damage to the containment casing and the engine, and is likely to pass completely through the containment casing. In contrast, if the blade remains within the plane of the fan, the entire chord length of the blade tip is generally impacted against the containment casing, enabling the kinetic energy of the blade to be more evenly distributed at the surface of the containment casing. Consequently, the blade is less likely to pierce the containment casing, such that the blade will remain contained within the containment casing.
Conventional containment casings are typically a solid metal casing having a thickness sufficient to withstand the impact of a fan blade within the plane of the fan. Protection provided by an outer shell formed from KEVLAR has also been used, for the purpose of exterior containment. However, blade containment achieved by these methods generally incurs significant additional weight, and/or does not sufficiently protect the interior surface of the containment casing, and/or does not offer sufficient protection to the containment casing forward of the fan, particularly in the event of a fan blade being propelled forward of the fan as described above.
Accordingly, it would be advantageous to provide an improved containment casing for turbomachinery, such as turbofan engines used in aerospace applications, wherein an interior protective barrier is provided for the containment casing so as to enhance the ability of the containment casing to withstand an impact by a released fan blade. Preferably, such a barrier would provide additional protection to the forward section of such machinery, and incur minimal additional weight.